Takahashi FS-85 Mini (visual) Review
Takahashi’s FSQ-85 is a popular deep-sky imaging scope, but this mini review focuses on using it visually. That’s because I haven’t yet had the opportunity to try imaging with it, but also because there’s not much info’ around on the visual performance of the FSQ-85. And it turns out that Takahashi have put lots of effort into making sure it works well with an eyepiece (unlike many imaging scopes).
This is the latest in a series of mini reviews of scopes that I’ve spent lots of time with, but haven’t been able to put through my complete review process.
I’ll hopefully be able to add example deep-sky images in due course.
(A big thanks to Richard Lynch for giving me access to his FSQs and for some of the images in this review).
At A Glance
450mm / 680mm w/ 1.5x extender
~370mm w/o visual back
Data from Tak, Me as usual.
Design and Build
Like the current FSQ-106 and FSQ-85, the original FSQ-106N was a quadruplet Petzval, but with a crown of mineral fluorite instead of the high-fluoride glass in the later ED models. That original version is distinguished by a longer OTA with a blue serial plate (below).
The FSQ-85ED, aka Baby-Q, came along later as a replacement for the discontinued doublet Sky90 portable imaging scope. There’s not much difference in size (or weight) between the Sky90 and the FSQ-85, but the FSQ-106 is much heavier.
Takahashi have now extended the ‘Q-for-quadruplet’ tag to two other scopes – the FS-60Q and FOA-60Q – but both are existing doublets with converter modules.
For a few years Takahashi also produced an FSQ-130ED, but it was hugely expensive.
The original fluorite FSQ-106N.
Three Takahashi imaging scopes: FSQ-106, FSQ-85 and FS-60C (actually an FS-60Q without its extender).
FSQs and Sky90.
The quadruplet Petzval was an early flat-field camera lens design later popularised for amateur telescopes by Al Nagler of Tele Vue, who developed a series them starting with the Genesis.
Compared with Tele Vue’s designs, Takahashi’s are more sophisticated in both optics and engineering, but the principal is the same.
The Petzval combines a long-focal-length objective with a doublet reducer/flattener at the rear that roughly halves the focal length. It’s a design that produces a fast and well-corrected optical system, but with the downside of vignetting (mitigated if the Petzval lens is expensively oversized, as it is in the 106 and Tele Vue’s imaging-system Nagler-Petzvals too).
In the case of the FSQ-85, the objective is a front-surface ED doublet of about ~F11, so the final focal length is 450mm (~F5.3). Unlike the Tele Vue Petzvals, both Takahashi’s ED variants employ a very large air gap between the Petzval elements to improve correction. The Petzval lens is mounted in the rear tube section in the 85.
So is the FSQ-85 just a scaled down FSQ-106ED, then? Not quite: it seems to a be a simpler design. Differences include:
· The FSQ-106ED has a more sophisticated objective with a larger air gap and collimation adjustment screws
· The FSQ-106ED uses two ED glass elements, one in the objective the other in the Petzval lens
· The FSQ-106ED’s larger Petzval lens gives better coverage (the front Petzval element isn’t much smaller than the objective!)
· The FSQ-106ED has a different tube design and a larger focuser
Overall, this means that the 106 has better coverage and smaller spot sizes (below) off-axis than the 85, possibly better correction too despite its larger aperture, but at much higher cost and almost double the weight.
Note: The original FSQ-85 was designed for imaging with an APS-C sized sensor and starts to suffer some residual field curvature and astigmatism by ~12mm off-axis. Consequently, Takahashi developed a dedicated 1.01X flattener for the FSQ-85 that gives good star images out to 22mm off-axis and 60% illumination as well.
The latest ‘EDP’ version (which has a slightly different focuser/rotator from the one here) ships with the Flattener in European markets.
The FSQ-85 has a 95mm tube like the FC-100D, with a 114mm diameter retracting dew shield. Build quality and finish is superb as usual.
Tak’ quote 535mm length with the dewshield retracted, but that’s with extension tubes fitted. With all the visual back components unthreaded, the FSQ-85 packs down to less than 400mm – shorter than a TV-85 or AP Stowaway and just a little longer than the tiny Sky-90. It’s easily carry-on portable.
The FSQ-85 feels weighty for its compact dimensions, but at 3.6 Kg it is much the same as other imaging apochromats in this size range.
In theory the tube separates into two sections on a threaded joint, but – unlike say an FC-100D – doesn’t need disassembly to fit in an airline case.
The focuser is a heavy duty rack-and-pinion unit, with a wide drawtube, a microfocuser, a larger pinion assembly than most and a camera-angle-adjuster, all standard equipment.
Tak’s focusers with their cast bodies and drawtubes are different from high-end units from the likes of Starlight Instruments made on a CNC machine. At their best, Takahashi’s are every bit as precise and perhaps even smoother, but can wear if subjected to heavy loads.
Despite being a robust unit, this one did exhibit just a little of the image shift that plagues some (but not all) Takahashi focusers, as usual likely the result of wear to the bushes.
On the night I did most of my viewing with the FSQ-85 it was mounted on a Vixen APZ – a small alt-az mount somewhere between a Porta and an AZ8. The combination was rock-solid, even at the highest powers, an advantage of a light and compact OTA like the FSQ.
For imaging, the FSQ-85 would be fine on a small equatorial, unlike its larger sibling.
The FSQ-85 shares the good-but-costly QE0.73x reducer with the FSQ-106. On the 85 it drops the focal length to just 327mm at F3.8 with an image circle of 60% at 44mm.
A cheaper option would be the 1.01x flattener which the new EDP model gets as standard. This offers the same 44mm/60% image circle as the reducer, but at 455mm focal length (F5.4) - sufficient for many.
For visual use, Takahashi offer a 1.5x extender (the FSQ-106’s gets a different 1.6x Extender-Q) to sharpen the optics and improve correction. It was used for the planetary viewing described in this review.
In Use – Daytime
As Tele Vue knew thirty years and more ago, flat-field Petzvals make great terrestrial scopes with their wide flat well-corrected field. Make no mistake, no prismatic scope gives the sharp, aberration-free high-power (100X plus) terrestrial views the FSQ-85 is capable of. My usual test of viewing silhouetted branches yields minimal fringing.
In Use – Observing the Night Sky
General Observing Notes
The FSQ-85 was very easy to use visually, with its short length and rotator allowing a comfy eyepiece position at all times. Cool down was fast (see below) compared with the larger scopes alongside and didn’t seem worse than the FC-100DC.
The focuser coped well with heavy eyepieces, but I did notice some image shift at high power on this example.
In terms of false colour and polychromatic-Strehl, the objective performs as I’d expect a regular 85mm F11 FPL-53 doublet should, which means very little false colour, no softness in the red and low bloat on hot stars for imaging.
I noted surprisingly rapid cool-down, in spite of the Petzval design which traps air between the elements. I also noted that the FSQ-106 alongside cooled much more gradually.
The star test was excellent, with evenly illuminated and spaced rings either side of focus and in-focus diffraction rings few and dim
The FSQ-85 gave exceptionally sharp and high-contrast views of limb mountains just after full Moon, picked out against black space with no false colour fringing and little flare.
Mars on opposition day 2022 showed a very sharply defined disk (17 arcsecs across) with the 4mm setting on Nagler Zoom giving 170x with the 1.5 extender. There was absolutely no false colour in or out of focus, no flare of dark red light that you often get with ED doublets and no softness.
I noted the dark area of Mare Acidalium in the north east. In the south, was a dark east-west strip comprising Mare Erythraeum in the east and Mare Sirenum in the west, with a lighter area in the middle that’s actually the Solis Lacus ‘Eye of Mars’ area, but not resolvable as such at this aperture.
I thought the view compared very favourably with the AP Stowaway’s the previous night, just slightly lower in contrast to the FC-100D on the same night (to be expected due to the smaller aperture).
The FSQ-85 gave a perfectly sharp, false-colour free view of Jupiter with the 5mm and 4mm settings on a Nagler Zoom giving 136x and 170x respectively. I noted lots of cloud belt detail, including thickness variations in NEB and SEB, polar cap banding and at least one other cloud belt. Very impressive for this aperture.
This is what prompted me to write this review, because I just hadn’t expected the FSQ-85 to perform well on planets at all.
Like Tele Vue’s Petzvals, when combined with a wide-field eyepiece like a Nagler, Delos or Ethos, the little FSQ has real wow factor for extended DSOs, with pinpoint stars across the whole flat field when turned on the Double Cluster and Stock2, or M36-38 in Auriga.
The Baby-Q gave an excellent split of the Double Double at 169x with the 4mm setting on the Nagler Zoom, with the small and perfect stellar diffraction patterns helping.
I expected the FSQ-85 to be a good imaging machine and knew it was small and compact, but I was surprised at what a fine visual scope it proved to be, even at high powers (albeit with the dedicated extender).
I was particularly surprised at the very fine planetary views it gave for an imaging refractor – very comparable to the AP Stowaway and significantly better on Mars than a TV-85.
Compared with some imaging scopes that are really just camera lenses, the FSQ-85 makes a fine double-duty tool for visual astronomy too, which could help justify its high price.
You knew the FSQ-85 produces good subs for imaging, but might be surprised at how well it performs visually, especially when combined with the dedicated extender.
FSQ-85 set on Mars at opposition.